This application is a 371 of PCT/JP00/08488 filed Dec. 1, 2000, now WO 01/40167.
The present invention relates to a method for producing an onium salt derivative useful as an onium-type strong-acid generator which generates a strong acid through irradiation with UV rays, a KrF excimer laser beam, an ArF excimer laser beam, an F2 excimer laser beam, an electron beam, or an X-ray; and to a novel onium salt derivative.
In recent years, in conjunction with a trend of high-density mounting of semiconductor devices, the wavelength of a light source used in a light-exposure apparatus employed in photolithographyxe2x80x94one of micro-processing methodxe2x80x94has been shortened. Recently, application of a KrF excimer laser beam (248.4 nm) has been investigated. Thus, resist material to be irradiated with a KrF excimer laser beam serving as a light source is required to possess high sensitivity to the exposed light so as to cause reaction.
In connection with this, a method using chemically amplified resist material is proposed (Polymn. Eng. Sci., Vol. 23, 1012 (1983)). According to the method, high sensitivity is attained by incorporating, into resist material, a compound which generates an acid through exposure to light.
Examples of the compound which generates an acid through exposure to light (hereinafter called an acid generator) and incorporated into the aforementioned chemically amplified resist material include onium salts such as diazoniumdiaryl salts, alkyliodoniumtriaryl salts, and alkylsulfonium salts, which are disclosed in a number of publications (e.g., in U.S. Pat. Nos. 4,491,628 and 4,603,101, Japanese Patent Publication (kokoku) No. 2-27660, and Japanese Patent Application Laid-Open (kokai) No. 62-1140).
Compounds such as 6-dinitrobenzyl tosylate are also disclosed as acid generators (e.g., F. I. Houliban et al., Advances in Resist Technology and Processing, SPIE, Vol. 920, 67, (1988)).
Among these acid generators, onium salts such as iodonium salts and sulfonium salts, inter alia, onium salt derivatives containing sulfonate as an anion, are widely used in view of their high stability of solution during storage.
There have been known methods for producing such onium salt derivatives, including salt exchange between an onium salt derivative containing a halide ion as an anion, and sulfonic acid, silver sulfonate, or alkali metal sulfonate (e.g., i J. Polymer Sci., Symposium No. 56, p. 383 (1976) and J. Rad. Curing, Vol. 4, p. 2 (1977)).
However, the above methods have drawbacks. Since exchange reaction between such an onium salt derivative and sulfonic acid or alkali metal sulfonate attains an equilibrium state, sulfonic acid or alkali metal sulfonate must be used in an amount of 1.5 mol-eq. or more based on the onium salt derivative containing a halide ion as an anion. In addition, migration of halide ions into the produced onium salt derivative containing sulfonate as an anion occurs. Furthermore, when a silver salt is used in the methods, cost for carrying out the reaction increases due to the high price of the silver salt.
Sulfonic acids which form these sulfonium salts serving as acid generators include a variety of species in terms of the substituent; from aromatic group to alkyl group. Therefore, it is preferable to obtain the sulfonic acids from a single common specific intermediate through anion exchange. However, since all sulfonic acids have an acidity stronger than that of sulfuric acid, sulfonate anions derived from the starting material unavoidably remain during a typical salt exchange process, due to equilibrium of the reaction, to thereby affect a resist containing the acid generators.
From another aspect, onium salt derivatives containing sulfonate as an anion are employed, for example, as thermal-polymerization or photo-polymerization initiators for a variety of anion-polymerizable compounds such as epoxy compounds and as photo-acid generators of chemically amplified resists.
In view of the foregoing, an object of the present invention is to provide a high-yield method for producing an onium salt derivative useful as an agent such as an acid generator used in chemically amplified resists. Another object of the invention is to provide a novel onium salt derivative.
The present inventors have carried out extensive studies in order to solve the aforementioned drawbacks, and have found that reacting an onium salt derivative containing a halide anion or a carboxylate anion with a sulfonic acid ester derivative or a phosphoric acid derivative can produce an onium sulfonate derivative or an onium phosphate derivative at high yield; that the reaction can provide a novel onium salt derivative containing phosphate as an anion; and that an onium salt derivative containing sulfonate as an anion can effectively be produced from the novel onium phosphate derivative. The present invention has been accomplished on the basis of these findings.
The present inventors have also found that a similar onium salt derivative containing sulfonate as an anion can be produced by reacting, in the presence of a specific compound such as an ortho acid ester, an onium salt derivative containing a halide anion or a carboxylate anion with a sulfonate salt. The present invention has been accomplished also on the basis of this finding.
Furthermore, the present inventors have also found that an onium sulfonate derivative can be produced at high yield by reacting an onium salt derivative containing a halide anion or a carboxylate anion with a sulfonic acid derivative such as dialkylsulfuric acid and, subsequently, with a sulfonate salt. The present invention has been accomplished also on the basis of this finding.
Accordingly, in a first mode of the present invention, there is provided a method for producing an onium salt derivative, characterized by comprising reacting an onium salt derivative represented by any one of formulas (1) through (4): 
wherein each of R1, R2, R3, and R5 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, an aralkyl group, or a phenacyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; one or both of the pairs of R1 and R3, and R2 and R5 may together form a divalent organic group; R4 represents a Cxe2x89xa620 divalent organic group; and Q represents a halide anion or a Cxe2x89xa610 carboxylate anion,
with a compound represented by any one of formulas (5) through (7): 
xe2x80x83wherein R6 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, or an aralkyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; R7 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, or an aralkyl group, each of these groups having xe2x89xa610 carbon atoms and being optionally substituted; and each of R8 and R9 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, or an aralkyl group, each of these groups having xe2x89xa610 carbon atoms and being optionally substituted,
to thereby yield an onium salt derivative represented by one of formulas (8) through (19). 
A second mode of the present invention is drawn to a specific mode of the first mode, and according to the second mode, there is provided a method for producing an onium salt derivative, wherein the sulfonic acid ester represented by formula (5) is a lower alkyl sulfonate in which R7 is a lower alkyl group having 5 or fewer carbon atoms.
A third mode of the present invention is drawn to a specific mode of the first or the second mode, and according to the third mode, there is provided a method for producing an onium salt derivative, wherein reaction is carried out while removing generated R7Q from the reaction system.
A fourth mode of the present invention is drawn to a specific mode of any one of the first through third modes, and according to the fourth mode, there is provided a method for producing an onium salt derivative, wherein the reaction is carried out in a solvent.
In a fifth mode of the present invention, there is provided a method for producing an onium salt derivative, characterized by comprising reacting an onium salt derivative represented by any one of formulas (1) through (4): 
wherein each of R1, R2, R3, and R5 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, an aralkyl group, or a phenacyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; one or both of the pairs of R1 and R3, and R2 and R5 may together form a divalent organic group; R4 represents a Cxe2x89xa620 divalent organic group; and Q represents a halide anion or a Cxe2x89xa610 carboxylate anion,
with a compound represented by any one of formulas (21) through (23): 
xe2x80x83wherein R10 represents hydrogen or an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, or an aralkyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; and each of R11, R12, and R13 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, or an aralkyl group, each of these groups having xe2x89xa610 carbon atoms and being optionally substituted;
and with a sulfonic acid derivative represented by formula (24):
R15SO2OYxe2x80x83xe2x80x83(24)
xe2x80x83wherein R15 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, or an aralkyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; and Y represents a hydrogen atom, an alkali metal, or ammonium,
to thereby yield an onium salt derivative represented by one of formulas (25) through (28). 
A sixth mode of the present invention is drawn to a specific mode of the fifth mode, and according to the sixth mode, there is provided a method for producing an onium salt derivative, wherein the compound represented by any one of formulas (21) through (23) is used in an amount by mol one to ten times that of the onium salt derivative represented by any one of formulas (1) through (4).
A seventh mode of the present invention is drawn to a specific mode of the fifth or the sixth mode, and according to the seventh mode, there is provided a method for producing an onium salt derivative, wherein the sulfonic acid derivative is used in an amount by mol one to two times that of the onium salt derivative represented by any one of formulas (1) through (4).
In an eighth mode of the present invention, there is provided a method for producing an onium salt derivative, characterized by comprising reacting an onium salt derivative represented by any one of formulas (1) through (4): 
wherein each of R1, R2, R3, and R5 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, an aralkyl group, or a phenacyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; one or both of the pairs of R1 and R3, and R2 and R5 may together form a divalent organic group; R4 represents a Cxe2x89xa620 divalent organic group; and Q represents a halide anion or a Cxe2x89xa610 carboxylate anion,
with a sulfuric acid ester represented by formula (29): 
xe2x80x83wherein each of R16 and R17 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, or an aralkyl group, each of these groups having xe2x89xa610 carbon atoms and being optionally substituted, to thereby form an onium salt derivative,
and reacting the resultant onium salt derivative with a sulfonic acid derivative represented by formula (24):
R15SO2OYxe2x80x83xe2x80x83(24)
xe2x80x83wherein R15 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, or an aralkyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; and Y represents a hydrogen atom, an alkali metal, or ammonium,
to thereby yield an onium salt derivative represented by one of formulas (25) through (28). 
A ninth mode of the present invention is drawn to a specific mode of the eighth mode, and according to the ninth mode, there is provided a method for producing an onium salt derivative, wherein the sulfuric acid ester represented by formula (29) is dimethylsulfuric acid or diethylsulfuric acid.
In a tenth mode of the present invention, there is provided a method for producing an onium salt derivative, characterized by comprising reacting an onium salt derivative represented by any one of formulas (12) through (15): 
wherein each of R1, R2, R3, and R5 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, an aralkyl group, or a phenacyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; one or both of the pairs of R1 and R3, and R2 and R5 may together form a divalent organic group; R4 represents a Cxe2x89xa620 divalent organic group; and each of R8 and R9 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, or an aralkyl group, each of these groups having xe2x89xa610 carbon atoms and being optionally substituted,
with a sulfonic acid derivative represented by formula (24):
R15SO2OYxe2x80x83xe2x80x83(24)
xe2x80x83wherein R15 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, or an aralkyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; and Y represents a hydrogen atom, an alkali metal, or ammonium,
to thereby yield an onium salt derivative represented by one of formulas (25) through (28). 
In an eleventh mode of the invention, there is provided a novel onium compound represented by any one of formulas (12) through (15): 
xe2x80x83wherein each of R1, R2, R3, and R5 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, an aralkyl group, or a phenacyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; one or both of the pairs of R1 and R3, and R2 and R5 may together form a divalent organic group; R4 represents a Cxe2x89xa620 divalent organic group; and each of R8 and R9 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, or an aralkyl group, each of these groups having xe2x89xa610 carbon atoms and being optionally substituted.
In the present invention, an onium salt derivative represented by any one of the aforementioned formulas (1) through (4), serving as a raw material, is reacted with an sulfonic acid ester, a phosphoric acid ester, or a sulfuric acid ester, to thereby produce an onium salt sulfonate derivative or an onium salt phosphate derivative at high yield.
Although the onium salt derivatives represented by formulas (1) through (4), serving as raw materials, include iodonium salts having a center element of iodine and sulfonium salts having a center element of sulfur, other onium salts, such as ammonium salts and phosphonium salts, may also be used.
Each of R1, R2, R3, and R5 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, an aralkyl group, or a phenacyl group, each of these groups having xe2x89xa625 carbon atoms and being optionally substituted; and one or both of the pairs of R1 and R3, and R2 and R5 may together form a divalent organic group. Specific examples of these substituents will be described hereinbelow.
Examples of the alkyl group include C3-C8 linear, branched, or cyclic alkyl groups. Specific examples include a methyl group, an ethyl group, a propyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, an iso-amyl group, a sec-amyl group, a 2-methylbutyl group, a 2-methyl-2-butyl group, a 1,1-dimethylbutyl group, 2-hexyl group, a 1,1,1-trimethylbenzyl group, a 1,1-dimethylhexyl group, a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group. Specific examples of the cycloalkyl group include C3-C20 cycloalkyl groups such as a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, and a bicycloheptyl group, and specific examples of the perfluoroalkyl group include a trifluoromethyl group,a perfluoropropyl group, a perfluorobutyl group, and a perfluorooctyl group.
Examples of the aromatic organic group include organic groups having a mono-ring or condensed ring carbon ring structure or having an aromatic nucleus of a mono-ring or condensed ring. Examples of the aromatic nucleus in the aromatic organic group include a phenyl group, a biphenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. These aromatic nuclei may have a substituent at an appropriate position. Examples of the substituent include C1-C12 alkyl groups (e.g., methyl, ethyl, propyl, butyl, and hexyl); C1-C12 alkoxy groups (e.g., methoxy, ethoxy, propoxy, and butoxy); C2-C11 acyl groups (e.g., acetyl and benzoyl); C2-C11 acyloxy groups (e.g., acetyloxy and benzoyloxy); C7-C20 aralkyl groups (e.g., benzyl, diphenylmethyl, and phenylpropyl); a nitro group; a cyano group; a butoxycarbonyloxy group; and halogen atoms (e.g., fluorine, chlorine, bromine, and iodine). The aromatic nuclei may have two or more different substituents.
Specific examples include aryl groups such as a phenyl group, a halogenated phenyl group, a hydroxyphenyl group, an alkoxyphenyl group, an aminophenyl group, an alkoxycarbonylphenyl group, a formylphenyl group, a thiophenyl group, a thioalkoxyphenyl group, and a cyanophenyl group.
Examples of the aralky group include C7-C20 aralkyl groups (e.g., benzyl, naphthylmethyl, anthranylmethyl, and diphenylmethyl). These aralkyl groups may have a substituent at an appropriate position of the aromatic nucleus, and examples of the substituent include those described in relation to the aforementioned aromatic organic group.
Specific examples include a phenylbenzyl group, a halogenated benzyl group, a hydroxybenzyl group, an alkoxyphenylbenzyl group, an aminobenzyl group, an alkoxycarbonylbenzyl group, a formylphenyl group, a thiobenzyl group, a thioalkoxybenzyl group, and a cyanobenzyl group.
Examples of R4 include divalent organic groups such as an arylene group, an alkylene group, a cycloalkylene group, and an aralkylene group. Specific examples include a phenylene group, a naphthylene group, an ethylene group, a propylene group, a butylene group, a hexylene group, a cyclohexylene group, and a xylylene group.
The divalent organic group which is formed by joining one or both of the pairs of R1 and R3, and R2 and R5 in formulas (3) and (4) is a divalent organic group which forms, in combination with a sulfur atom in the compound represented by formula (3) or (4), an aliphatic or an aromatic heterocyclic structure. Examples of such divalent organic groups include organic groups represented by the following formulas.
xe2x80x83xe2x80x94(CH2)4xe2x80x94 xe2x80x94(CH2)5xe2x80x94 xe2x80x94(CH2)2O(CH2)2xe2x80x94
Q represents a halide anion or a Cxe2x89xa610 carboxylate anion.
Examples of the halide anion include a fluoride ion, a chloride ion, a bromide ion, and an iodide ion.
The carboxylate anion is selected from the group represented by the following formula (20):
R19xe2x80x94COOxe2x8ax96xe2x80x83xe2x80x83(20)
wherein R19 represents hydrogen or an alkyl group which has 10 or fewer carbon atoms and being optionally substituted. An alkyl group having 5 or fewer carbon atoms is preferred.
Compounds represented by formulas (5) through (7) which are to be reacted with an onium salt derivative represented by any one of formulas (1) through (4) are sulfonate esters, phosphate esters, and sulfate esters, respectively.
Specific examples of R6 through R9 are provided hereinbelow.
R6 represents an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, or an aralkyl group; each of which is optionally substituted and has 25 or fewer carbon atoms. Specific examples of R6 are provided hereinbelow.
Examples of the alkyl group include optionally substituted C1-C20 alkyl groups such as methyl, ethyl, propyl, butyl, and hexyl.
Examples of the perfluoroalkyl group include trifluoromethyl, nonafluorobutyl, and perfluorooctyl.
Examples of the cycloalkyl group include C3-C15 cycloalkyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, bicycloheptyl, and 7,7-dimethyl-2-oxo-bicyclo[2,2,1]heptane-1-methyl.
Examples of the aromatic organic group include C6-C25 aromatic organic groups such as phenyl, tolyl, trimethylphenyl, isopropylphenyl, triisopropylphenyl, t-butylphenyl, fluorophenyl, bis(trifluoromethyl)phenyl, difluorophenyl, trifluorophenyl, trifluoromethylphenyl, pentafluorophenyl, naphtyl, anthryl, 9,10-dimethoxyanthryl, and phenanthryl.
Examples of the aralkyl group include C7-C20 aralkyl groups such as benzyl, naphtylmethyl, anthranylmethyl, and diphenylmethyl.
Each of R7, R8, and R9 represents an alkyl, a cycloalkyl, a perfluoroalkyl, or an aralkyl group; each of which is optionally substituted and has 10 or fewer carbon atoms. An alkyl group having 5 or fewer carbon atoms is particularly preferred.
Although the reaction of the present invention can be carried out in the presence or absence of a solvent, the reaction is preferably carried out in the presence of a solvent. Examples of the solvent to be used include halogenated hydrocarbons such as dichloromethane, chloroform, carbon tetrachloride, and chlorobenzene; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, and di-t-butyl ether; and nitriles such as acetonitrile and benzonitrile, with ethers being preferred.
No particular limitation is imposed on the reaction temperature of the present invention, and a range of 0xc2x0 C.-200xc2x0 C. is preferred.
The reaction of the present invention is transesterification, and compounds represented by R7xe2x80x94Q (e.g., alkyl halides) are formed. Preferably, R7xe2x80x94Q is removed from the reaction system. Thus, the lower the boiling point of R7xe2x80x94Q, the easier the removal thereof. In an example method of removing R7xe2x80x94Q formed through the reaction, a solvent having a boiling point higher than that of R7xe2x80x94Q is employed and the reaction is carried out at a temperature higher than the boiling point of R7xe2x80x94Q for vaporization and removal of R7xe2x80x94Q.
The onium salt derivatives represented by formulas (8) through (19) produced through the above-described method can be used, without additional treatment, as agents such as acid generators. Alternatively, in accordance with needs, the onium salt derivatives may be used after being subjected to salt exchange reaction through a customary method. In particular, the onium salt sulfonate derivatives of formulas (16) and (17) are useful as onium-type strong-acid generators; which generate strong acid particularly through irradiation with UV rays, KrF excimer laser beams, ArF excimer laser beams, F2 excimer laser beams, electron beams, or X-rays.
The onium salt phosphate derivatives represented by formulas (12) through (15) are novel compounds. They are onium having, as a counter ion to the onium moiety, a conjugated base of a weak acid (i.e., phosphate ester) as an anion moiety. Such an onium salt per se may be used as an acid generator. However, since such an onium salt readily undergoes salt exchange reaction with a strong acid such as sulfonic acid, there can be obtained an onium salt derivative having, as a counter ion to the onium moiety, a conjugated base of sulfonic acid, in a form free of impurities such as halogens.
When the onium salt phosphate derivative is produced by the aforementioned method of the present invention, the reaction may be carried out under the aforementioned reaction conditions. However, particularly suitable reaction conditions are provided hereinbelow.
A suitable amount of a phosphate ester for synthesis of the onium salt phosphate derivative is within a range of 1-3 equivalents, preferably 1.2-2 equivalents, based on 1. equivalent of a starting onium salt. In a case where the phosphate ester is employed as a solvent, a suitable amount of the phosphate ester is a range of 5-30 equivalents, more preferably 10-20 equivalents, based on 1 equivalent of the starting onium salt.
A suitable amount of a reaction solvent is within a range of 1-20 liters (hereinafter represented by xe2x80x9cLxe2x80x9d), preferably 5-10 L, based on 1 equivalent of the starting onium salt. Typically, a phosphate ester represented by formula (6) is employed as a reaction solvent. In other words, the phosphate ester represented by formula (6) serves not only as a reaction reagent but also as a reaction solvent. When the reaction of the present invention is carried out in the presence of a solvent, the species of the solvent is not particularly limited. Solvents such as a hydrocarbon solvent, a chlorine-containing solvent, an alcohol solvent, an ether solvent, a nitrile solvent, and an ester solvent may be used appropriately. Solvents of higher boiling point, such as 1,2-dichloroethane and dioxane, are preferred.
The reaction temperature typically falls within a range of 40-200xc2x0 C., preferably 50-80xc2x0 C. Unnecessarily higher temperature may cause a side reaction, resulting in a lower yield of the target compound. In contrast, lower reaction temperature prolongs the reaction time.
The reaction time typically falls within a range of 1 minute to 40 hours, preferably 5 minutes to 20 hours. Although the staring onium salts are insoluble at an initial period of the reaction, they dissolve as the reaction proceeds. However, diphenyliodonium chloride has very low solubility in solvents. In the case where a phosphate ester is used, upon cooling of the reaction mixture after completion of reaction, an onium salt crystallizes out. The crystallized onium salt is washed with a small amount of a solvent, such as alcohol, ether, or acetone, and then dried. The resultant compound may be used without any additional treatment when the compound is to be used for salt exchange reaction.
Although most onium phosphates are soluble in water, onium sulfonate salts formed through salt exchange reaction are taken up in an organic layer through extraction. In addition to equilibrium shift due to strong acidity, the sulfonate salts can be produced with nearly complete selectivity. The aforementioned production method of an onium phosphate utilizes the following reaction; i.e., a trialkyl phosphate undergoes nucleophilic substitution reaction, in which a halide serving as a nucleophilic agent reacts with an alkyl group of the trialkylphosphate, resulting in formation of a haloalkane, which is removed from the reaction system, thus facilitating the anion exchange. Thus, the production method is very effective.
Furthermore, when the above-described onium salt phosphate derivative serving as a starting material is reacted with the sulfonate salt represented by formula (24), the required amount of sulfonic acid can be reduced, and the yield of the target onium sulfonate derivative can be improved.
According to the method of the present invention, an onium dialkylphosphate is particularly preferred as the starting material. Salt exchange reaction thereof with a sulfonic acid forms an alkylphosphoric acid, which exhibits, in an aqueous solution, pKa of approximately 2. Since sulfonic acid exhibits a pKa of xe2x88x923 to xe2x88x926, which is greatly different from 2, the equilibrium shifts substantially toward the onium sulfonate salt.
In the method of the present invention, sulfonic acid is used in an amount of 1-2 mol, preferably 1.05-1.2 mol, based on 1 mol of the onium phosphate. The reaction solvent is used in an amount of 1-20 L, preferably 5-10 L, based on 1 mol of the onium salt.
In general, a halogen-containing solvent (e.g., methylene chloride or chloroform) is employed as a reaction solvent. However, any solvent may be used so long as it can form a separate layer from an aqueous layer and can dissolve an onium salt as a solute.
The reaction temperature is typically room temperature. The reaction time is not particularly limited, since the exchange reaction occurs instantaneously.
After completion of the reaction, the reaction mixture is alkalinized by adding water and an aqueous alkaline solution (e.g., an aqueous solution containing an amine such as ammonia), to thereby facilitate the exchange reaction and to facilitate the transfer of remaining acid to the aqueous layer. After removal of the aqueous layer, the organic layer is washed with water several times until pH is lower to a neutral region. The thus-obtained mixture is dried; the solvent is removed through distillation, and the residue is purified by treatment such as recrystallization, to thereby obtain a target compound.
Phosphate salts have a considerably low acidity as compared with a typical sulfonic acid and are usually water-soluble. In contrast, onium sulfonates formed via salt exchange are taken up into an organic layer through extraction. Thus, according to the method of the present invention, the acid equilibrium shifts toward the sulfonate salt, enabling production of a target compound in the form of sulfonate salt at nearly perfect selectivity.
According to the present invention, an onium salt derivative represented by any one of formulas (1) through (4), a compound represented by any one of formulas (21) through (23), and a sulfonate salt represented by formula (24) are cause to react in one step, to thereby produce an onium sulfonate salt at high yield.
The compounds represented by formulas (21) through (23) are orthocarboxylate esters, phosphate esters, and sulfate esters, respectively. R10 in formula (21) is a hydrogen atom, or has the same meaning as the aforementioned substituent group R6. Each of R11 to R13 of the compounds represented by formulas (21) through (23) has the same meaning as the aforementioned substituent groups R7 and R8.
R15 of the sulfonate salt represented by formula (24) is an alkyl group, a cycloalkyl group, a perfluoroalkyl group, an aromatic organic group, or an aralkyl group; each having 25 or fewer carbon atoms and being optionally substituted. Specific examples of R15 are provided hereinbelow.
Examples of the alkyl group include optionally substituted C1-C20 alkyl groups such as methyl, ethyl, propyl, butyl, and hexyl.
Examples of the perfluoroalkyl group include trifluoromethyl, nonafluorobutyl, and perfluorooctyl.
Examples of the cycloalkyl group include C3-C15 cycloalkyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, bicycloheptyl, and 7,7-dimethyl-2-oxo-bicyclo[2,2,1]heptane-1-methyl.
Examples of the aromatic organic group include C6-C25 aromatic organic groups such as phenyl, tolyl, trifluoromethylphenyl, pentafluorophenyl, naphtyl, anthryl, 9,10-dimethoxyanthryl, and phenanthryl. Examples of the aralkyl group include C7-C20 aralkyl groups such as benzyl, naphtylmethyl, anthranylmethyl, and diphenylmethyl.
In formula (24), Y represents a hydrogen atom; an alkali metal such as lithium, sodium, or potassium; and/or ammonium. The group xe2x80x9cammoniumxe2x80x9d herein is represented by formula (31): 
wherein each of R20 to R23 represents hydrogen, an alkyl group, an aralkyl group, or an aryl group.
The reaction involving such compounds and sulfonate salts is presumed to smoothly proceed via the following steps. the aforementioned sulfonate compound is decomposed by acid catalytic action of sulfonic acid, to thereby yield cations. The formed cations are reacted with anions such as halide anions, to thereby form compounds such as alkyl halides. Thus, anions such as halide anions are removed, and, in turn, the sulfonic acid undergoes salt exchange reaction.
According to the above-described method of the present invention, a compound such as an ortho acid ester is used in an amount by mol of 1-10 times, preferably 1.2-5 times, that of the onium salt derivative.
The sulfonate salt is used in an amount by mol of 1-2 times, preferably 1.05-1.2 times, that of the onium salt derivative.
An appropriate solvent is employed in the reaction, and examples thereof include a chlorine-containing solvent, an alcohol solvent, an ether solvent, a nitrile solvent, an ester solvent, and a carboxylic acid solvent. Of these, methylene chloride and chloroform are particularly preferred.
Although the reaction generally proceeds at room temperature, the reaction can be accelerated by heating. Typically, the reaction temperature is not greater than 100xc2x0 C., and preferably falls within a range of 40-60xc2x0 C.
The reaction time depends on the reaction temperature. Reducing the anion concentration such as a halide anion concentration to not greater than 50 ppm requires 12 hours (at room temperature), or 2-4 hours (at 40xc2x0 C.).
After completion of the reaction, the reaction mixture is alkalinized by adding aqueous ammonia. Subsequently, the target compound is taken up from the reaction solvent used through extraction. The thus-obtained solution is dried, the solvent is removed through evaporation, and the residue is recrystallized.
The above-described method of the present invention can provide onium sulfonates containing halides, which are detrimental to resist processes, at extremely low concentrations. Therefore, the onium sulfonates are useful as acid generators for chemically amplified resists.
Alternatively, according to the present invention, an onium salt derivative represented by any one of formulas (1) through (4) is reacted with a sulfate ester represented by formula (29), followed by reaction with a sulfonate ester represented by (24), to thereby yield an onium salt derivative having, as a counter ion to the onium moiety, a conjugated base of sulfonic acid. Such a method provides the target onium salt derivative of high purity in a simple, cost-effective manner.
The substituents R16 and R17 of formula (29) have the same meanings as R7 and R8 of formula (7). However, each of R16 and R17 is preferably an alkyl group having 5 or fewer carbon atoms, most preferably a methyl group and an ethyl group.
The above-described method of the present invention includes a first step comprising reaction of an onium salt derivative represented by any one of formulas (1) through (4) (hereinafter, description is provided on the assumption that the onium salt derivative contains a halogen serving as an anion), serving as a starting material, with a sulfate ester such as dialkylsulfuric acid (hereinafter, description is provided on the assumption that the sulfate ester is an alkyl ester). The first step yields an onium salt derivative having a monoalkylsulfate ion serving as a counterion.
This step is presumed to proceed in the following manner in which a halide-anion-containing onium salt derivative is reacted with a dialkylsulfuric acid, to thereby yield an alkyl halide and an onium salt derivative containing a monoalkylsulfate ion serving as a counter ion. Thus, halide anions can be removed from the reaction system by removing the alkyl halide formed through the reaction. The dialkyl sulfuric acid preferably has lower alkyl groups, with dimethyl sulfuric acid and/or diethyl sulfuric acid being particularly preferred. When a dialkyl sulfuric acid having lower alkyl groups is employed, the resultant substances, such as alkyl halide, can be vaporized and readily removed from the reaction system.
Although the first step may be carried out in the presence or absence of a solvent, this step is preferably carried out in the presence of a solvent. Examples of the solvent to be used include halogenated hydrocarbons such as dichloromethane, chloroform, carbon tetrachloride, and chlorobenzene; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, and di-t-butyl ether; and nitriles such as acetonitrile and benzonitrile. No particular limitation is imposed on the reaction temperature, and a range of 30-120xc2x0 C. is preferred, with 40-100xc2x0 C. being particularly preferred.
When an onium salt derivative having a halide anion as an anion moiety is reacted with a dialkylsulfuric acid, no particular limitation is imposed on the mol ratio of the onium salt derivative having a halide anion as an anion moiety to the dialkylsulfuric acid. However, a mol ratio within a range of 1.0: 1.0-2.0 is preferred. When the mol ratio of the dialkylsulfuric acid is lower than 1.0:1.0, halide anions disadvantageously remain after completion of the reaction. The dialkylsulfuric acid may be used in a mol ratio of 2.0 or more. However, the greater the amount of employed dialkylsulfuric acid, the greater the amount of unreacted dialkylsulfuric acid.
In a second step, the onium salt derivative prepared in the first step and having, as a counter ion to the onium moiety, a conjugated base of a monoalkylsulfuric acid is reacted with a sulfonic acid and/or an alkali metal salt thereof and/or an ammonium salt thereof, to thereby yield a target onium salt derivative having, as a counter ion to the onium moiety, a conjugated base of a sulfonic acid. The sulfonic acid and salts thereof employed in the second step are represented by the aforementioned formula (24).
When the onium salt derivative having, as a counter ion to the onium moiety, a conjugated base of a monoalkylsulfuric acid is reacted with a sulfonic acid and/or a salt thereof in the second step of the present invention, no particular limitation is imposed on the mol ratio of the onium salt derivative having, as a counter ion to the onium moiety, a conjugated base of a monoalkylsulfuric acid to the sulfonic acid and/or a salt thereof. However, a mol ratio within a range of 1.0: 1.0-1.5 is preferred. Although the mol ratio may be 1.0 or less, the yield of the target onium salt derivative having, as a counter ion to the onium moiety, a conjugated base of a sulfonic acid disadvantageously decreases. Although the mol ratio may be 1.5 or more, using a large excess amount of the sulfonic acid and/or a salt thereof is economically disadvantageous.
Although the reaction of the second step of the present invention may be carried out in the presence or absence of a solvent, the reaction is preferably carried out in the presence of a solvent. Examples of the solvent include water, halogenated hydrocarbons such as dichloromethane, chloroform, carbon tetrachloride, and chlorobenzene; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, and di-t-butyl ether; and nitrites such as acetonitrile and benzonitrile. Of these, water is preferred. A mixed solvent containing water and the above-described organic solvent is also preferred. No particular limitation is imposed on the reaction temperature of the second step.